1. Field of the Invention
The invention relates to a technique for protecting against electrocution or shock. More specifically, the invention relates to a circuit and method for terminating the supply of power to an exposed conductor when a part of a human body contacts the conductor.
2. Description of the Prior Art
A number of known circuits interrupt the supply of power to a normally-energized conductor when the conductor is contacted by a part of a human body. U.S. Pat. No. 3,997,818, issued to L. E. Bodkin, discloses a circuit for protecting against electrocution by switching off the supply of power whenever a body or other improper load permits current to flow in a direction opposite the normal current direction. The normal current direction is maintained by a rectifier such as a diode. By doubling the circuit, an alternating current may be used. When a current flow in the reverse direction is detected, a thyristor or silicon-controlled rectifier (SCR) is turned off, switching off the flow of power.
U.S. Pat. No. 3,781,608, issued to E. Geiger, discloses a similar circuit which detects a short circuit through the discharge of a capacitor. Upon detection of a short circuit, a thyristor is disabled, and a reduced current flows.
It would be advantageous to have a protection technique capable of interrupting power when a human body touches an exposed conductor in response to effects other than a flow of current due to the application of full power. The known prior art circuits all depend, to some extent, on a flow of current through the human body before power is interrupted, and it would be beneficial to provide a circuit in which such a flow of current is unnecessary.
In addition, it would be advantageous to provide such a technique which could be used with an exposed conductor which ordinarily provides power to a device in contact with it.